High temperature superconductors and cars – it doesn't get any cooler (seriously)

Ok, so I’m going to go about this in the fashion most often called ‘arse-about-face’.

An HTS motor

First, a word of explanation. I was lucky enough to get to go to the ISIS-18 open day a little while back. During said day, I developed what is probably going to be a lifelong fascination with all things high temperature superconductor-ish. I went to the day knowing very little about the subject, and left knowing somewhat more factually, and a great deal more just in terms of how madly interesting the field is.

Hence the arse-about-face bit. I want to do a series of posts looking into various issues, facts, stories etc about high temperature superconductor (HTS) technology. And so, I should begin with a proper introduction, enlightening you all as to the basics and whatnot. This is not going to happen. It will actually take the form of the second post in the series.

The first post is going to be about their use in cars. And why? Because I think it’s seriously, seriously cool. And it all came about when I got talking to the guys from Sumitomo about their fun project and persuaded them to send me their research so that I could bore the pants off you, dear readers.

Regarding HTS, the only basic thing you need to know for now is that some metals*, when cooled to seriously frostbite-inducing temperatures, become superconducting. This means that they are able to conduct electricity with no resistance. None whatsoever. Which is awesome. It’s apparently a quantum mechanical phenomenon (but what isn’t these days?), and one we’re still pretty far from properly understanding (more on that in the next post). ‘Conventional’, or low temperature, superconductors were the first kind we discovered – about 100 years ago – and have to be chilled to between 1K and 20K (-272.15 deg. C to -253.15 deg. C). Which is very, very cold and chews a great deal of power and effort.

HTS, on the other hand, have raised this minimum temperature as high as 92K (-181.15 deg. C). Yes, it’s still very cold, but it takes far less power to do and, excitingly, means that liquid nitrogen can be used as a coolant – a far easier coolant to produce and use than the liquid helium used by LTS.

And it’s an exciting technology for both environmental and economic reasons. Due to the vastly increased efficiency at which HTS wires can transmit electricity, there is a corresponding decrease in power loss – this means less electricity needs to be generated to reach the same output, which makes everyone happy.

Now, on to the point of the post:

While at ISIS-18 I got talking to some chaps from Sumitomo Electric, a company in Japan, who have been having a little bit of laddish fun with HTS. Specifically, they’ve been playing around with a car (formerly a golf cart, hilariously) and HTS tech. Said car, which is obviously electric, contains a motor in which HTS wire has been used (more on that later). Now, everyone knows that HTS motors in cars is never going to be a practical application: ships and huge trucks yes, but cars, no. Instead, this is a proof of concept thing. And an excuse a) for the Sumitomo brains to play, and b) for the CEOs of Japan’s various car companies to drive around in seriously next-gen tech. I know I certainly would…

There isn’t much known at the moment on the use of HTS tech in land vehicles; people have primarily been looking at their use in the huge motors of ships. Certainly, however, there is a need for increasingly environmentally-friendly land vehicles of all kinds, given the issue of global warming and our contribution thereto. Currently, there are three main types of environmentally-friendly vehicles being developed:

HEV’s are pretty widespread, and have been since the late 1990s. They’re also spreading far faster than the other two types of car, for what I hope are pretty obvious reasons: cost, convenience and availability. Many people are heralding, however, that once we get a good grip on FCV technology, they’ll overtake the other two kinds.

The important thing to note with all of three types of car is that they use electricity. Which is where HTS comes in. How does it do this?

Well, the motor is a standard series-wound DC motor, but HTS wire gets used for the motor coil instead of ‘normal’ wire. This coil is then kept immersed in liquid nitrogen. For those of you who understand, and are interested in such terms, this superconducting coil provides a much higher flux density, and therefore delivers higher torque. There are also other advantages, which can be seen in the diagram below:

Advantages conferred by HTS motor

To explain the ‘no transmission’ bit: because of the much higher torque supplied by HTS motors, one wouldn’t need the variable-speed gears used by other engines to deal with the huge range in rpm. This means that the motor could directly drive the wheel shaft, hence cutting down on transmission loss. There’s a picture below as well, if it helps.

System configuration

Now, there have to be challenges, right? And yes, there are.

The big one is, obviously, keeping everything cold enough. This means that the motor needs some sort of refrigeration mechanism, which itself needs to be powered. As a result, it’s best to use this kind of motor in cars/vehicles which are heavily used, for a couple of reasons: if they’re kept going, they can provide the power to keep the refrigeration going, and also, in the words of the paper itself:

“In a heavy vehicle that requires a high output, the output of the cooling mechanism has less impact on the increase of motor efficiency and the decrease of transmission loss. Furthermore, because high output is required during acceleration or deceleration regeneration of a heavy vehicle, superconducting motors would also be suitable for buses and other mass-transit vehicles that experience frequent stop-and-go operations”.

Couldn’t have put it better meself.

Of course, if we can get to the point where liquid hydrogen could be used as a coolant, then things will get even more exciting. Imagine, if you will: in FCVs, liquid hydrogen might well be part-and-parcel of the car’s operating system. Due to some of the properties of superconducting wire, the use of liquid hydrogen (which is far colder than liquid nitrogen) means that superconducting wire would become even more superconducting, meaning more current and higher torque. It would also mean that cooling system could be downsized or even left out altogether, making things both more efficient and cheaper (yay).

So how does our prototype car run?

Well, better than its golf cart predecessor, that’s for sure. The car in question is a retrofitted Toyota Probox, which is your bog-standard gasoline car, and everything got put in as shown below.

Configuration of superconducting car

Something I thought was quite interesting was that the car can accelerate from a standstill, effortlessly, while in 3rd gear! For those who’ve ever stalled their car in 3rd, this is a prospect capable, I am sure, of causing frissons of delight. Apparently, it’s because the highest torque in electric cars is obtained at the lowest speeds.

Apparently, in the 6 months before this paper came out, the car was run for about 200km, and showed no issues. At a top speed of 70km/hr, it’s hardly zippy, but it does show what’s possible. And it makes me happy 🙂

The car in question

Addendum: if anyone’s seriously interested in the exact specs of the engine, I’m happy to provide 🙂

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